Decomposition of Arsine and Trimethylarsenic on GaAs Investigated by Surface Photo-Absorption

The decomposition processes of arsine (AsH₃) and trimethylarsenic (TMAs) on a GaAs surface are investigated in situ in an MOCVD reactor by the surface photo-absorption (SPA) method. This method is based on measuring the reflectivity of p-polarized light incidence at the Brewster angle. Small changes in reflectivity at the surface can be detected with a high signal-to-noise ratio. When 325-nm He-Cd laser light is used during Ga deposition on an As surface, the reflectivity increases in proportion to the Ga coverage and saturates after the complete growth of one Ga atomic layer. When the AsH₃supply in resumed, the reflectivity drops and approaches the initial value of the As surface as As coverage increases. Therefore, the decomposition of As precursors on a GaAs substrate surface can be studied by observing the decay in reflection intensity. From the substrate temperature dependence of decay lifetime, activation energies were calculated to be 17 kcal/mol and 65 kcal/mol for AsH₃and TMAs, respectively. These results suggest that the catalytic effect of the GaAs surface reduces the decomposition energy in AsH₃, much more than in TMAs.